The film's based on a memoir by Colin Clark [played by Eddie Redmayne], who was Laurence Olivier's assistant on the movie and who, during an intense period of filming, became Marilyn Monroe's confidant.

But he flirted with Lucy as much as possible in between takes. Clark described Lucy as 'one of the prettiest little girls I have ever seen in my life... slim as a wand, curly brown hair, huge brown eyes and a wide cheeky grin.'

Harvey told me: 'For ten years she has been this schoolgirl in the Harry Potter films and now you see her as a woman for the first time.

'She has an elegance about her - she looks like Jean Shrimpton! - plus she has a gift for comedy and drama, and we're just starting to see her range.

'I feel we're going to work together a lot in the future.'